1. Field of the Invention
The present invention relates to gaskets and other insertable members for sealing or placement between component parts of various equipment. More particularly, the present invention relates to gaskets and other apparatus which monitor the seal or other conditions between component parts and detect leaks or other problems therebetween.
2. Description of Related Art
A wide variety of gaskets of different shapes, sizes and properties have been developed for particular applications. For example, U.S. Pat. Nos. 3,783,173 issued Jan. 1, 1974, to Twomey, and 4,966,637 issued Oct. 30, 1990, to Laborie each discloses electrically conductive gaskets; U.S. Pat. No. 5,112,664 issued May 12, 1992, to Waterland, III, discloses a gasket made from expanded polytetrafluoroethylene (PTFE) for use in corrosive environments.
In each instance, the gaskets serve to seal between component parts of various equipment and/or to reduce wear between component parts. Among the more common materials used in gaskets today are various elastomers (e.g. VITON fluoroelastomer, nitrile rubber, ethylene-propylene-diene monomer (EPDM) rubber, various fluoropolymers (e.g. polytetrafluoroethylene (PTFE), expanded PTFE (ePTFE)), fluorinated ethylenepropylene (FEP), perfluoroalkoxy polymer (PFA), polyvinylidene fluoride (PVDF)). The growing use of more durable materials, such as ePTFE, has greatly improved gasket operative life and reliability.
Despite improvements in the quality and operative life of gaskets, the risk and cost of gasket failures remains substantial. First, gaskets must be properly installed and maintained to assure full operational life. In this regard, insufficient or excessive torque applied against the gasket in installation can lead to leakage and/or premature gasket failure. Applying the correct amount of torque generally requires expensive equipment or subjective experience achieved through trial-and-error. Even the proper use of a torque wrench provides only an indirect measurement of the amount of pressure which is actually applied to the gasket material.
Likewise, seals between component parts should be periodically checked for leakage which may indicate cracks or wear in the gasket. Such inspections may be important to avoid a catastrophic gasket failure during normal operation and all the costs inherent in such a failure, such as potential equipment damage, excessive down-time, and costly and possibly dangerous leaks and spills. Additionally, the replacement of gaskets is often an important reason for scheduled maintenance procedures, with the schedule of frequent maintenance sometimes being a function of anticipated timing for gasket replacement.
A number of these problems are discussed in U.S. Pat. No. 4,969,105 issued Nov. 6, 1990, to Gaenssle. This patent addresses the problem that the process of tightening a gasket tends to compress the gasket material and leave gaps through which leaks can occur. The problem of loosening of the seal around the gasket is addressed by Gaenssle by providing a feedback system monitoring the amount of torque which must be applied to a gasket in order to keep it adequately compressed. Unfortunately, this system has a number of deficiencies. First, the use of a dedicated torque-producing drive system is considered far too expensive and complicated for most gasket applications. Second, this system does not provide monitoring of the overall condition of the gasket itself. Third, this system does not address applications where component parts are not attached around a gasket by bolts or similar torque producing means.
U.S. Pat. No. 5,121,929 issued Jun. 16, 1992, to Cobb also attempts to provide feedback on the amount of load applied to a gasket. In this patent an electronic load sensor comprising discrete electrodes and pressure sensitive electrically resistive material is sealed within a cavity in the body of the gasket. While this device may function adequately in its intended harsh environments, it is believed that this device is overly complex and expensive to manufacture for widespread use. Additionally, this gasket does not attempt to address the concerns of detection of leaks due to gasket breakage or similar failure.
Although equipment exists which can monitor the pressure between component parts for other applications, and theoretically could be used to assure correct installation and operation of gaskets, generally such equipment is likewise far too expensive and/or fragile to be practical for most applications. For example, U.S. Pat. No. 3,358,257 issued Dec. 12, 1967, to Painter et al. discloses a force and moment transducer employing semiconductor piezoresistive ribbons in two or four arm active bridge circuits to measure forces between equipment and support structure, such as in the aerospace service environment. Although such equipment may work well for its intended uses, such a device cannot provide true gasketing function and is considered too complicated, bulky, and expensive to monitor gasket seals in common applications.
In yet another usage U.S. Pat. No. 4,781,535 issued Nov. 1, 1988, to Frawley et al. a continuous electrical circuit trace is applied across most of the surface of a diaphragm for a diaphragm pump. The circuit trace serves to measure both continuity of the diaphragm and potential ground fault condition between the circuit trace and pumping liquid. While this device may be effective at monitoring a pump diaphragm for leaks, it does not address the problems inherent with gasket maintenance, much less the desire for a reliable way to monitor compression forces applied during the installation of a gasket.
Accordingly, it is a primary purpose of the present invention to produce a gasket or other insertable member which contains reliable means to verify its structural integrity during installation and operation and to determine conditions between component parts between which the insertable member is installed.
It is a further purpose of the present invention to provide such a member which is durable, and relatively inexpensive and easy to construct, install, and operate.
It is yet another purpose of the present invention to produce a gasket which can be adapted to monitor the compressional forces applied against it to assure proper installation and seal.
It is another purpose of the present invention to employ recent advances in conductive fiber technology to produce a seal-verifying gasket with improved operational properties.
These and other purposes of the present invention will become evident from review of the following specification.